Microscopic estimation of the deformation potential in a structural model glass

Starting from a microscopic Hamiltonian we analyze the coupling between tunneling systems (TS's) and phonons in a structural model glass, chosen to describe NiP. We estimate the TS-phonon coupling constants, i.e., the longitudinal and transverse deformation potentials γₗ and γₜ. They are proportional to the spatial distance between the two energy minima. This dependence translates into an energy dependence of the deformation potential, which is relevant for the temperature dependence of the low-temperature thermal conductivity. On the basis of TS's in NiP found via a computer search in our previous work we obtain the values γₗ=0.38 eV and γₗ²/γₜ²{}2.35. We analyze the influence of the structure of typical TS's on the deformation potential. Together with the density of tunneling systems determined in a previous paper the interaction between tunneling systems can be calculated. In contrast to recent proposals, the weak-coupling picture and hence the validity of the standard tunneling model is confirmed.